qt: Fix headers

This change is preparation for Qt 6, and it fixes an experimental build
with Qt 6.2.4.

src/qt/bitcoingui.cpp

@@ -41,6 +41,7 @@
 #include <validation.h>
 
 #include <QAction>
+#include <QActionGroup>
 #include <QApplication>
 #include <QComboBox>
 #include <QCursor>

src/qt/guiutil.cpp

@@ -60,6 +60,7 @@
 #include <QSettings>
 #include <QShortcut>
 #include <QSize>
+#include <QStandardPaths>
 #include <QString>
 #include <QTextDocument> // for Qt::mightBeRichText
 #include <QThread>

src/qt/walletview.cpp

@@ -23,7 +23,6 @@
 #include <util/strencodings.h>
 
 #include <QAction>
-#include <QActionGroup>
 #include <QFileDialog>
 #include <QHBoxLayout>
 #include <QProgressDialog>